Forming tunneling field-effect transistor with stacking fault and resulting device

ABSTRACT

Methods for forming stacking faults in sources, or sources and drains, of TFETs to improve tunneling efficiency and the resulting devices are disclosed. Embodiments may include designating areas within a substrate that will subsequently correspond to a source region and a drain region, selectively forming a stacking fault within the substrate corresponding to the source region, and forming a tunneling field-effect transistor incorporating the source region and the drain region.

TECHNICAL FIELD

The present disclosure relates to tunneling field-effect transistors(TFETs). The present disclosure is particularly applicable to formingTFETs for the 20 nanometer (nm) technology node and beyond.

BACKGROUND

To avoid the 60 millivolt (mV) per decade sub-threshold slope limit,carriers within a field-effect transistor (FET) must not go over the P/Njunction barrier. Band-to-band (BTB) tunneling that occurs in TFETs isnot subjected to this limit because the carriers do not flow over apotential barrier. Rather, the carriers tunnel through the barrier.However, TFETs suffer from low drive current as a result of poortunneling efficiency.

A need therefore exists for a method of providing improved tunnelingefficiency in TFETs, and the resulting device.

SUMMARY

An aspect of the present disclosure is a method of forming stackingfaults in sources, or sources and drains, of TFETs to improve tunnelingefficiency.

Another aspect of the present disclosure is TFETs with increasedtunneling efficiency based on stacking faults in sources, or sources anddrains.

Additional aspects and other features of the present disclosure will beset forth in the description which follows and in part will be apparentto those having ordinary skill in the art upon examination of thefollowing or may be learned from the practice of the present disclosure.The advantages of the present disclosure may be realized and obtained asparticularly pointed out in the appended claims.

According to the present disclosure, some technical effects may beachieved in part by a method including designating areas within asubstrate that will subsequently correspond to a source region and adrain region, selectively forming a stacking fault within the substratecorresponding to the source region, and forming a tunneling field-effecttransistor incorporating the source region and the drain region.

An aspect of the present disclosure includes forming another stackingfault within the substrate corresponding to the drain region. Anotheraspect of the disclosure includes creating tensile stress within thesubstrate to form the stacking fault. Yet an additional aspect of thedisclosure includes selectively forming an amorphization implant maskabove the substrate exposing the source region to form the stackingfault. A further aspect includes, where the substrate is formed ofsilicon, forming a transition between an amorphous state and acrystalline state of the silicon to form the stacking fault. Additionalaspects include doping the source region and the drain region to form asource and a drain, respectively, of the TFET, and forming an inverselydoped pocket in the source. Another aspect includes forming theinversely doped pocket above the stacking fault and underneath a gate ofthe TFET. Yet another aspect includes forming the stacking fault acrosssubstantially an entire thickness of the source region.

Another aspect of the present disclosure is a device including: TFETincluding: a substrate, a source and a drain within the substrate, agate between the source and the drain, and a stacking fault within thesource.

An aspect includes the TFET including a stacking fault within the drain.Another aspect includes the stacking fault within the source beingtensile stress within the substrate. Another aspect includes thestacking fault being is formed using an amorphization implant mask toselectively expose the source. Additional aspects include the substratebeing formed of silicon, and the stacking fault formed as a transitionbetween an amorphous state and a crystalline state of the silicon. Yetanother aspect includes an inversely doped pocket in the source. Stillanother aspect includes the inversely doped pocket being formed abovethe stacking fault and underneath the gate. An additional aspectincludes the stacking fault extending across substantially an entirethickness of the source.

According to the present disclosure, additional technical effects may beachieved in part by a method including: forming a stacking fault in aregion of a silicon substrate, doping the region of the siliconsubstrate, forming a source, doping another region of the siliconsubstrate, forming a drain, and forming a TFET incorporating the sourceand the drain.

Further aspects of the present disclosure include selectively formingthe stacking fault in the region by forming an amorphization implantmask above the region of the silicon substrate. Yet another aspect ofthe present disclosure includes forming a transition between anamorphous state and a crystalline state of the silicon substrate to formthe stacking fault. Still another aspect of the present disclosureincludes forming an inversely doped pocket in the source above thestacking fault and underneath the gate of the tunneling field-effecttransistor.

Additional aspects and technical effects of the present disclosure willbecome readily apparent to those skilled in the art from the followingdetailed description wherein embodiments of the present disclosure aredescribed simply by way of illustration of the best mode contemplated tocarry out the present disclosure. As will be realized, the presentdisclosure is capable of other and different embodiments, and itsseveral details are capable of modifications in various obviousrespects, all without departing from the present disclosure.Accordingly, the drawings and description are to be regarded asillustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIGS. 1 through 2B illustrate a method for forming TFETs with stackingfaults in the source, or source and drain, regions, in accordance withan exemplary embodiment; and

FIGS. 3A through 3G illustrate a specific method for forming stackingfaults in the source, or source and drain, regions in TFETs, inaccordance with an exemplary embodiment.

DETAILED DESCRIPTION

In the following description, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of exemplary embodiments. It should be apparent, however,that exemplary embodiments may be practiced without these specificdetails or with an equivalent arrangement. In other instances,well-known structures and devices are shown in block diagram form inorder to avoid unnecessarily obscuring exemplary embodiments. Inaddition, unless otherwise indicated, all numbers expressing quantities,ratios, and numerical properties of ingredients, reaction conditions,and so forth used in the specification and claims are to be understoodas being modified in all instances by the term “about.”

The present disclosure addresses and solves the current problem of lowdrive current attendant upon TFETs. In accordance with embodiments ofthe present disclosure, stacking faults are formed in the source, or thesource and drain, regions of the TFETs to effectively narrow the silicon(Si) band gap to enhance BTB tunneling efficiency.

Methodology in accordance with an embodiment of the present disclosureincludes designating an area within a substrate that will subsequentlycorrespond to a source region, or areas within a substrate that willsubsequently correspond to a source region and a drain region. Stackingfaults are then selectively formed in the source region, or the sourceand drain regions, causing tensile stress within the substrate. Thestacking fault may be a transition between an amorphous state and acrystalline state of the substrate, such as Si, that narrows the Si bandgap and reduces the drive current.

Adverting to FIG. 1, a method for forming stacking faults in sources, orsources and drains, of TFETs to improve tunneling efficiency, accordingto an exemplary embodiment, begins with an n-type TFET (NTFET) 100 a anda p-type TFET (PTFET) 100 b. Although illustrated as beingdiscontinuous, the NTFET 100 a and the PTFET 100 b may be formed withina single, continuous substrate. The NTFET 100 a is formed of asemiconductor substrate 101 a, which may include any semiconductormaterial such as Si, germanium (Ge), silicon germanium (SiGe), siliconcarbide (SiC), silicon-on-insulator (SOI), or SiGe-on-insulator (SGOI).The substrate 101 a may include a lightly n-doped region 103 a, a sourceregion 105 a, and a drain region 107 a. The source region 105 a may bep-doped and the drain region 107 a may be n-doped. However, the sourceregion 105 a and the drain region 107 a may merely be regions designatedwithin the substrate 101 a that are later doped to form sources anddrains, such that the regions are not necessarily already doped.

Further, the NTFET 100 a includes a gate stack formed of an oxide layer109 a and a gate layer 111 a above the substrate 101 a. The gate oxidelayer 109 a may be formed of any gate oxide material, such as silicondioxide (SiO₂), and the gate layer 111 a may be formed of any type ofgate material. Although not shown (for illustrative convenience), thegate stack may instead be formed of a dummy gate, such as of polysilicon(poly-Si), for subsequent removal and formation of a replacement metalgate. Below the gate stack and between the source region 105 a and thedrain region 107 a is a channel 113 a.

The PTFET 100 b is formed of a semiconductor substrate 101 b, which mayinclude any semiconductor material such as Si, Ge, SiGe, SiC, SOI, orSGOI. The substrate 101 b may include a lightly n-doped region 103 b, ap-well region 103 c, a source region 105 b and a drain region 107 b. Thesource region 105 b may be n-doped and the drain region 107 b may bep-doped. However, the source region 105 b and the drain region 107 b maymerely be regions within the substrate 101 a that are later doped suchthat, as illustrated in FIG. 1, the regions are not necessarilypre-doped.

Further, the PTFET 100 b includes a gate stack formed of an oxide layer109 b and a gate layer 111 b above the substrate 101 b. The gate oxidelayer 109 b may be formed of any gate oxide material, such as SiO₂, andthe gate layer 111 b may be formed of any type of gate material.Although not shown (for illustrative convenience), the gate stack mayinstead be formed of a dummy gate, such as of poly-Si, for subsequentremoval and formation of a replacement metal gate. Below the gate stackand between the source region 105 b and the drain region 107 b is achannel 113 b.

Although not required, the source regions 105 a and 105 b may havepocket regions 115 a and 115 b, respectively, to further improve asurface tunneling junction between the source regions 105 a and 105 band the channels 113 a and 113 b, respectively. The pocket regions 115 aand 115 b may be above subsequently formed stacking faults 201 and belowthe gate stacks. Within the source region 105 a the pocket region 115 ais n-doped, and within the source region 105 b the pocket region 115 bis p-doped. The pocket regions 115 a and 115 b improve the junctionbetween the source regions 105 a and 105 b and the channels 113 a and113 b, respectively, for the NTFET 100 a and PTFET 100 b.

Adverting to FIG. 2A, the NTFET 100 a and the PTFET 100 b aresubsequently processed to form stacking faults 201 a and 201 b in thesource regions 105 a and 105 b, respectively. Alternatively, asillustrated in FIG. 2B, the NTFET 100 a and the PTFET 100 b aresubsequently processed to also form stacking faults 203 a and 203 b inthe drain regions 107 a and 107 b, respectively, in addition to thesource regions 105 a and 105 b. The stacking faults 201 a and 201 b (aswell as stacking faults 203 a and 203 b, if present) can be transitionsbetween an amorphous state and a crystalline state of a siliconsubstrate. The stacking faults 201 a and 201 b improve tunnelingefficiency by effectively narrowing down the Si band gap as a result ofthe tensile stress within the Si caused by the stacking faults 201 a and201 b near the junction between the source regions 105 a and 105 b andthe channels 113 a and 113 b, respectively. The narrowing of the Si bandgap induces high BTB tunneling or gate-induced drain leakage (GIDL),causing higher orders of junction leakage. Specifically, at the p-dopedsource region 105 a in the NTFET 100 a, the stacking fault 201 a narrowsdown the Si band gap at the P+/N tunneling junction between the sourceregion 105 a and the channel 113 a. At the n-doped source region 105 bin the PTFET 100 b, the stacking fault 201 b narrows down the Si bandgap at the N+/P tunneling junction between the source region 105 b andthe channel 113 b.

The stacking faults may be formed in the source regions 105 a and 105 band the drain regions 107 a and 107 b according to any stressmemorization technique that forms stress, such as tensile stress, in thesubstrate 101 a and 101 b. FIGS. 3A through 3G illustrate a specificmethod for forming the stacking faults according to one stressmemorization technique. As illustrated in FIG. 3A, a pre-amorphizationimplantation mask 301 is formed over the NTFET 100 a and PTFET 100 billustrated in FIG. 1. The pre-amorphization implantation mask 301 maybe conformally formed over the NTFET 100 a and PTFET 100 b. Thepre-amorphization implantation mask 301 is used to selectively formopenings 303 a and 303 b corresponding to the respective locations wherethe stacking faults 201 a and 201 b are formed in the NTFET 100 a andthe PTFET 100 b. To form the stacking faults 203 a and 203 b,corresponding openings may be made in the pre-amorphization implantationmask 301 (not shown for illustrative convenience).

Next, an oxide layer 305 is formed over the pre-amorphizationimplantation mask 301, as illustrated in FIG. 3B. The oxide layer 305may be formed of any oxide, such as SiO₂, to a thickness of for example40 Å. The oxide layer 305 may be formed according to various techniques,such as conformally depositing the oxide layer 305 over thepre-amorphization implantation mask 301. The oxide layer 305 fills theopenings 303 in the pre-amorphization implantation mask 301 and comesinto contact with the substrates 101 a and 101 b.

A silicon nitride (SiN) layer 307 is then formed over the oxide layer305, as illustrated in FIG. 3C. The SiN layer 307 may be formed to athickness of for example 400 Å, and may be conformally deposited overthe oxide layer 305, such as by plasma enhanced chemical vapordeposition (PECVD).

After forming the SiN layer 307, the resulting structures are heated atfor example 650° C., for 10 minutes, for example, in an inertatmosphere, such as in the presence of nitrogen gas (N₂). The resultingstructure and heat treatment causes stacking faults to form in thesubstrates 101 a and 101 b corresponding to the openings 303 a and 303 bin the pre-amorphization implantation mask 301 as a result of tensileand compressive stress within the substrates 101 a and 101 b, asillustrated in FIG. 3D.

Subsequently, the SiN layer 307 is then removed, as illustrated in FIG.3E. The SiN layer 307 may be removed by the application of a layer ofhot phosphorous. The oxide layer 305 is then removed, as illustrated inFIG. 3F. The oxide layer 305 may be removed by the application of alayer of dilute hydrofluoric acid (dHF). Subsequently, thepre-amorphization implantation mask 301 is stripped according to anyconventional technique, as illustrated in FIG. 3G. The result is a NTFET100 a and a PTFET 100 b (as illustrated in FIG. 2A). Subsequentprocessing may then proceed in further forming the NTFET 100 a and thePTFET 100 b, such as forming raised sources and drains, implanting thesource regions 105 a and 105 b and the drain regions 107 a and 107 b andforming replacement metal gates. Accordingly, the method described abovewith respect to FIGS. 3A through 3G can be implemented in forming any Sicomplementary metal-oxide-semiconductor (CMOS) in the formation ofTFETs.

The embodiments of the present disclosure achieve several technicaleffects, including effectively narrowing down the Si band gap to enhanceBTB tunneling efficiency while being fully compatible with current SiCMOS technology without adding extra process complexity. As discussedabove, the embodiments of the present disclosure can be furtheroptimized with other improvements to TFETs, such as junction design orhetero-structures to even further increase tunneling efficiency. Thepresent disclosure enjoys industrial applicability associated with thedesigning and manufacturing of any of various types of highly integratedsemiconductor devices used in microprocessors, smart phones, mobilephones, cellular handsets, set-top boxes, DVD recorders and players,automotive navigation, printers and peripherals, networking and telecomequipment, gaming systems, and digital cameras. The present disclosuretherefore enjoys industrial applicability in any of various types ofsemiconductor devices, particularly in the 20 nm technology node andbeyond.

In the preceding description, the present disclosure is described withreference to specifically exemplary embodiments thereof. It will,however, be evident that various modifications and changes may be madethereto without departing from the broader spirit and scope of thepresent disclosure, as set forth in the claims. The specification anddrawings are, accordingly, to be regarded as illustrative and not asrestrictive. It is understood that the present disclosure is capable ofusing various other combinations and embodiments and is capable of anychanges or modifications within the scope of the inventive concept asexpressed herein.

What is claimed is:
 1. A method comprising: designating areas within asubstrate that will subsequently correspond to a source region and adrain region; selectively forming a stacking fault within the substratecorresponding to the source region; forming a tunneling field-effecttransistor incorporating the source region and the drain region; dopingthe source region and the drain region to form a source and a drain,respectively, of the tunneling field-effect transistor; and forming aninversely doped pocket in the source.
 2. The method according to claim1, further comprising: forming another stacking fault within thesubstrate corresponding to the drain region.
 3. The method according toclaim 1, comprising: creating tensile stress within the substrate toform the stacking fault.
 4. The method according to claim 1, furthercomprising: selectively forming an amorphization implant mask above thesubstrate exposing the source region to form the stacking fault.
 5. Themethod according to claim 1, wherein the substrate is formed of silicon,the method comprising: forming a transition between an amorphous stateand a crystalline state of the silicon to form the stacking fault. 6.The method according to claim 1, comprising: forming the inversely dopedpocket above the stacking fault and underneath a gate of the tunnelingfield-effect transistor.
 7. The method according to claim 1, comprising:forming the stacking fault across substantially an entire thickness ofthe source region.
 8. A method comprising: forming a stacking fault in aregion of a silicon substrate; doping the region of the siliconsubstrate, forming a source; doping another region of the siliconsubstrate, forming a drain; forming a tunneling field-effect transistorincorporating the source and the drain; and forming an inversely dopedpocket in the source above the stacking fault and underneath the gate ofthe tunneling field-effect transistor.
 9. The method according to claim8, further comprising: selectively forming the stacking fault in theregion by forming an amorphization implant mask above the region of thesilicon substrate.
 10. The method according to claim 8, comprising:forming a transition between an amorphous state and a crystalline stateof the silicon substrate to form the stacking fault.